The persistent rainfall that fell in Catalonia in January 202 led to tragic situations, such as the Gelida rail accident caused by the collapse of a retaining wall, as well as landslides in other parts of the commuter network. We speak with Dr Núria M. Pinyol, a researcher in CIMNE’s Geomechanics and Hydrogeology research cluster and an expert in geotechnical engineering, about the factors behind these events and the measures that can help prevent such risks.
Retaining walls are key elements in many types of infrastructure, as they allow for differences in ground level, particularly along roads, railways and uneven terrain. When the ground is very strong, such as solid rock, it is possible to cut almost vertically without adding external support. But when working with less cohesive soils, as is often the case in road and rail construction, retaining walls come into play. They are designed to withstand the forces exerted by the ground behind them and ensure the stability of the structure. As Dr Pinyol explains, one of the critical factors affecting the integrity of retaining walls is water infiltration. When the soil behind the wall becomes saturated, the water exerts additional pressure that the wall must resist. For this reason, designs include drainage systems that allow water to be discharged. However, if these drains fail for any reason, pressures can rise to the point of causing structural collapse. Moreover, during periods of intense and prolonged rainfall, such as those experienced in Catalonia in January 2026, water not only increases the load on the wall but also reduces the strength of the soil behind it, adding further risk factors.
“If the drains fail for any reason, pressures can rise to the point of causing structural collapse.”
As Pinyol notes, wall failures rarely occur due to a single, isolated cause. They are usually the result of a combination of factors: water pressure, structural issues such as reinforcement corrosion or excessive cracking, and even landslides beyond the wall that can compromise the entire structure. “The challenge with geotechnics is that it’s not easy to see what’s going on, because everything is buried underground,” the CIMNE researcher explains. This makes early detection essential: sometimes small cracks, seepage or slight movements are the only visible signs of a problem that could become serious.
“The challenge with geotechnics is that it’s not easy to see what’s going on, because everything is buried.”
To prevent such risks, Dr Pinyol highlights the importance of visual inspections and, in particular, monitoring systems. Installed at critical points, these systems enable real-time, remote tracking of wall conditions, sending data to centralised databases and triggering alerts when anomalies are detected.
Numerical methods: a cornerstone of geotechnical prevention
Numerical modelling has proven to be a fundamental tool in geotechnics. In the specific case of retaining walls, it can help anticipate what may happen under different scenarios: from the implementation of preventive measures to assessing how risk may evolve in the short and medium term, taking into account factors such as climate change and shifting rainfall patterns. Collaboration between the scientific community and public authorities, such as the Department of Territory of the Government of Catalonia, is essential to ensure proper management of geotechnical assets and the safety of infrastructure.
